1. Field of the Invention
The present invention relates to an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject (e.g., a ratio of an inferior-limb blood pressure to a superior-limb blood pressure, or a ratio of a superior-limb blood pressure to an inferior-limb blood pressure), and to an apparatus for measuring a blood pressure of an inferior limb of a living subject, the latter apparatus being advantageously employed by the former apparatus.
2. Related Art Statement
For a person who suffers arterial obstruction or arteriostenosis, his or her inferior-limb blood pressure (xe2x80x9cBPxe2x80x9d) value is lower than his or her corresponding superior-limb BP value (for example, a systolic superior-limb BP value corresponds to a systolic inferior-limb BP value). Meanwhile, if an inferior-limb BP value of a person is higher than his or her corresponding superior-limb BP value by a prescribed value, he or she may suffer aortic incompetence or aortitis syndrome limited to aortic arch. It has been practiced to utilize this for diagnosing arterial disease based on the ratio of inferior-limb BP value to superior-limb BP value or the ratio of superior-limb BP value to inferior-limb BP value, that is, a superior-and-inferior-limb BP index.
Since the superior-and-inferior-limb BP index is simply obtained as the ratio of inferior-limb BP value-to superior-limb BP value or the ratio of superior-limb BP value to inferior-limb BP value, it is required to measure accurately the inferior-limb BP value. However, if one or more blood vessels running in a portion of an inferior limb from which the inferior-limb BP value is measured suffer advanced calcification, that is, sclerosis of tunica media as the middle one of three layers of tunica vasculosa, the inferior-limb BP value is raised because of the hardness of the blood vessels. In addition, since an inferior limb is thicker than a superior limb and has a generally conical shape, it is hard to wind an inflatable cuff around it. Moreover, since arterial vessels running in an inferior limb are present deep in adipose tissues and muscles, it is naturally harder to measure an inferior-limb BP value than measure a superior-limb BP value. In the case where blood vessels running in a portion of an inferior limb from which an inferior-limb BP value is measured suffer highly advanced calcification, those blood vessels cannot be fully occluded by the pressing of an inflatable cuff and accordingly an excessively high inferior-limb BP value may be measured. Therefore, if a person who suffers arterial obstruction or arteriostenosis also suffers advanced calcification of his or her inferior-limb blood vessels, a normal superior-and-inferior-limb BP index value may be measured from the person. In this case, arterial obstruction or arterio-stenosis cannot be accurately diagnoses based on the superior-and-inferior-limb BP index.
It is therefore an object of the present invention to provide an apparatus which can measure a highly reliable superior-and-inferior-limb blood-pressure index of a living subject even if he or she may suffer the calcification of his or her inferior-limb blood vessels.
It is another object of the present invention to provide an apparatus which measures a superior-and-inferior-limb blood-pressure index of a living subject while judging whether the measurement of an inferior-limb blood pressure is abnormal.
It is another object of the present invention to provide an apparatus which measures an inferior-limb blood-pressure of a living subject while judging whether the subject suffers the calcification of his or her inferior-limb blood vessel.
(1) According to a first feature of the present invention, there is provided an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising a first blood-pressure measuring device which measures a first blood pressure of a right inferior limb of the subject; a second blood-pressure measuring device which measures a second blood pressure of a left inferior limb of the subject; a third blood-pressure measuring device which measures a third blood pressure of a superior limb of the subject; a first information obtaining device which obtains first information relating to a first velocity of propagation of a first pulse wave which propagates through a first route a portion of which runs in the right inferior limb; a second information obtaining device which obtains second information relating to a second velocity of propagation of a second pulse wave which propagates through a second route a portion of which runs in the left inferior limb; selecting means for selecting one of the measured first and second blood pressures that corresponds to one of the first and second information that relates to a lower one of the first and second velocities; and index determining means for determining the superior-and-inferior-limb blood-pressure index, based on the selected one of the first and second blood pressures, and the measured third blood pressure.
According to this feature, the first information obtaining device obtains first information relating to a first velocity of propagation of a first pulse wave which propagates through a first route a portion of which runs in the right inferior limb, the second information obtaining device obtains second information relating to a second velocity of propagation of a second pulse wave which propagates through a second route a portion of which runs in the left inferior limb, the selecting means selects one of the measured first and second BP values that corresponds to one of the first and second information that relates to a lower one of the first and second velocities, and the index determining means determines the superior-and-inferior-limb BP index, based on the selected one of the first and second BP values, and the measured third BP value. The higher the degree of calcification of blood vessel is, the higher the velocity of propagation of pulse wave through the blood vessel is. Therefore, the selected one of the measured first and second BP values that corresponds to the lower one of the first and second velocities, means the inferior-limb BP value measured from the less calcified inferior limb. Since this inferior-limb BP value, selected by the selecting means, is used in determining the superior-and-inferior-limb BP index, a highly reliably superior-and-inferior-limb BP index value can be obtained.
(2) According to a second feature of the present invention that includes the first feature (1), the index determining means comprises means for determining, as the superior-and-inferior-limb blood-pressure index, a ratio of the selected one of the first and second blood pressures to the third blood pressure, or a ratio of the third blood pressure to the selected one of the first and second blood pressures.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the first information obtaining device comprises two first pulse-wave sensors which are worn on two different first portions of the living subject, respectively, and each of which detects the first pulse wave at a corresponding one of the two first portions, at least one of the two first portions belonging to the right inferior limb, and the second information obtaining device comprises two second pulse-wave sensors which are worn on two different second portions of the subject, respectively, and each of which detects the second pulse wave at a corresponding one of the two second portions, at least one of the two second portions belonging to the left inferior limb.
(4) According to a fourth feature of the present invention that includes the third feature (3), the first information obtaining device comprises first time determining means for determining, based on respective times when the two first pulse-wave sensors detect the first pulse wave, a first propagation time needed for the first pulse wave to propagate between the two different first portions of the living subject, and the second information obtaining device comprises second time determining means for determining, based on respective times when the two second pulse-wave sensors detect the second pulse wave, a second propagation time needed for the second pulse wave to propagate between the two different second portions of the subject.
(5) According to a fifth feature of the present invention that includes the fourth feature (4), the first information obtaining device comprises first velocity determining means for determining, based on the determined first propagation time and a distance between the two first portions of the living body, the first velocity of propagation of the first pulse wave, and wherein the second information obtaining device comprises second velocity determining means for determining, based on the determined second propagation time and a distance between the two second portions of the living body, the second velocity of propagation of the second pulse wave.
(6) According to a sixth feature of the present invention, there is provided an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising a first blood-pressure measuring device which includes a first inflatable cuff adapted to be wound around an inferior limb of the subject and which measures a first blood pressure of the inferior limb; a second blood-pressure measuring device which measures a second blood pressure of a superior limb of the subject; a first pulse-wave sensor which detects a first pulse wave which propagates through a portion of the inferior limb that is located on an upstream side of the first inflatable cuff; sharpness determining means for determining a degree of sharpness of a heartbeat-synchronous pulse of the first pulse wave detected by the first pulse-wave sensor; and judging means for judging that when the determined degree of sharpness is not greater than a first reference value and the measured first blood pressure is higher than the measured second blood pressure by a value not smaller than a second reference value, the measurement of the first blood pressure by the first blood pressure measuring device is abnormal.
According to this feature, the sharpness determining means determines a degree of sharpness of a heartbeat-synchronous pulse of the first pulse wave detected by the first pulse-wave sensor, and the judging means judges that when the determined degree of sharpness is not greater than a first reference value and the measured first blood pressure is higher than the measured second blood pressure by a value not smaller than a second reference value, the measurement of the first-blood pressure by the first blood pressure measuring device is abnormal. Thus, an operator such as a medical staff can recognize that the measurement of the first blood pressure has not been properly performed by the first blood pressure measuring device. A small degree of sharpness, determined by the sharpness determining means, means that the subject suffers arteriostenosis in the portion of the inferior limb located on the upstream side of the first inflatable cuff and accordingly a lowered BP value is measured from a portion of the inferior limb located on a downstream side of the cuff. If it is assumed that the BP measurement has been properly performed, the determined degree of sharpness which is not greater than the first reference value should mean that the measured inferior-limb BP value is equal to, or lower than the superior-limb BP value. When, in fact, the measured inferior-limb BP value is higher than the superior-limb BP value by a value not smaller than the second reference value, it can therefore be concluded that the BP measurement was abnormal because the blood blow through the blood vessel or vessels running in the portion of the inferior limb pressed by the cuff cannot be fully stopped by the cuff.
(7) According to a seventh feature of the present invention that includes the sixth feature (6), the second blood-pressure measuring device comprises a second inflatable cuff adapted to be wound around the superior limb of the subject, and wherein the apparatus further comprises a second pulse-wave sensor which detects a second pulse wave which propagates through a portion of the superior limb that is located on an upstream side of the second inflatable cuff; and reference-value determining means for determining the first reference value based on the second pulse wave detected by the second pulse-wave sensor.
(8) According to an eighth feature of the present invention that includes the sixth or seventh feature (6) or (7), the sharpness determining means comprises means for determining, as the degree of sharpness, a percentage, %MAP, of a height of a center of gravity of an area enveloped by a waveform of the heartbeat-synchronous pulse of the first pulse wave, relative to an amplitude of the waveform of the pulse.
(9) According to a ninth feature of the present invention, there is provided an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising a first blood-pressure measuring device which includes an inflatable cuff adapted to be wound around an inferior limb of the subject and which measures a first blood pressure of the inferior limb; a second blood-pressure measuring device which measures a second blood pressure of a superior limb of the subject; a first pulse-wave sensor which detects a first pulse wave which propagates through a portion of the inferior limb that is located on an upstream side of the inflatable cuff; a second pulse-wave sensor which detects a second pulse wave which propagates through the superior limb; and a display device which simultaneously displays the measured first and second blood pressures and the detected first and second pulse waves.
According to this feature, the display device simultaneously displays the measured first and second blood pressures and the detected first and second pulse waves. Therefore, if the first or inferior-limb BP value is higher than the second or superior-limb BP value but an observer can see on the display device that the first or inferior-limb pulse wave is less sharp than the second or superior-limb pulse wave, the observer can judge that the BP measurement peformed by the first or inferior-limb BP measuring device was abnormal.
(10) According to a tenth feature of the present invention that includes the ninth feature (9), the apparatus further comprises index determining means for determining a superior-and-inferior-limb blood-pressure index of the subject, based on the measured first and second blood pressures, and the display device displays the determined superior-and-inferior-limb blood-pressure index, in addition to the measured first and second blood pressures and the detected first and second pulse waves.
(11) According to an eleventh feature of the present invention, there is provided an apparatus for measuring a blood pressure of an inferior limb of a living subject, comprising a blood-pressure measuring device which includes an inflatable cuff adapted to be wound around the inferior limb and which measures, with the cuff, the blood pressure of the inferior limb of the subject; an input device which is operable for inputting at least one characteristic value characteristic of the subject and which produces at least one signal representing the at least one input characteristic value; map selecting means for selecting, based on the input characteristic value, one of a plurality of predetermined maps each of which defines, in a coordinate system having a first axis representing blood pressure and a second axis representing information relating to velocity of propagation of pulse wave through blood vessel, a calcification range indicating calcification of the blood vessel; an information obtaining device which obtains information relating to a velocity of propagation of a pulse wave which propagates between two different portions of the subject that include a portion of the inferior limb around which the inflatable cuff is wound; and judging means for judging whether the measured blood pressure and the obtained information fall in the calcification range of the selected map, and thereby judging whether at least one blood vessel running in the portion of the inferior limb has been calcified to such a degree that a blood flow through the blood vessel cannot be stopped by the inflatable cuff.
According to this feature, the map selecting means selects, based on the input characteristic value, one of a plurality of predetermined maps each of which defines, in a coordinate system having a first axis representing blood pressure and a second axis representing information relating to velocity of propagation of pulse wave through blood vessel, a calcification range indicating calcification of the blood vessel, and the judging means judges whether the measured blood pressure and the obtained information fall in the calcification range of the selected map, and thereby judges whether at least one blood vessel running in the portion of the inferior limb has been calcified to such a degree that a blood flow through the blood vessel cannot be stopped by the inflatable cuff. Therefore, an operator can recognize that the BP measurement performed by the BP measuring device was abnormal.
(12) According to a twelfth feature of the present invention that includes the eleventh feature (11), the input device comprises means for inputting, as the at least one characteristic value, at least one value selected from the group consisting of an age of the subject, a value corresponding to a sex of the subject, and a height of the subject.
(13) According to a thirteenth feature of the present invention that includes the eleventh or twelfth feature (11) or (12), the apparatus further comprises a memory which stores the plurality of predetermined maps.
(14) According to a fourteenth feature of the present invention that includes any one of the eleventh to thirteenth features (11) to (13), the information obtaining device comprises propagation-time measuring means for measuring a time needed for the pulse wave to propagate between the two different portions of the subject.
(15) According to a fifteenth feature of the present invention that includes the fourteenth feature (14), the information obtaining device further comprises inverse-of-propagation-time determining means for determining, as the information, an inverse of the propagation time measured by the propagation-time measuring means.